Rosenberg et al. established in 1961 that when a microcrystalline powder of β-carotene is sandwiched between 2 sheets of electrodes, and the electric conductivity of the powder of β-carotene is measured in various gases, the electric conductivity of the powder of β-carotene is remarkably increased in gases that are sensed by us as odor such as ethanol, ammonia or acetone (for example, see Non-Patent Document 1).
Generally, oxide semiconductor odor sensors that utilize oxide semiconductors are known. An oxide semiconductor odor sensor is a device that utilizes a mechanism to detect the variation of the resistance value of the semiconductor caused by the adsorption/reaction of odor molecules on the surface of the semiconductor. Among oxide semiconductor odor sensors, some oxide semiconductor odor sensors have been developed in such a way that the oxide semiconductors are heated with a heater at high temperatures (about 500° C.) to eliminate the effects of the ambient temperature/humidity; however, such sensors are complex in structure, can hardly be reduced in size, and is high in production cost.
Additionally known are quartz oscillator odor sensors that utilize the mechanism of the variation of the resonant frequency of the quartz oscillator caused by the adsorption of odor molecules on the quartz oscillator.
Non-Patent Document 1: Hiroshi Asai, “Odor Detectors,” Solid State Physics (Kotai Butsuri in Japanese), Vol. 10, No. 7, pp. 369-373 (1975).
Non-Patent Document 2: Mitachi, Kondo, Sasaki, and Sugimoto, “Selection of Optimal Desiccants for Use in Odor Sensors,” The 50th Spring Meeting of Japan Society of Applied Physics and Related Societies, 29p-B-13 (Mar. 29, 2003).